package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.File;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.BufferUnderflowException;
import java.nio.channels.ClosedChannelException; // javadoc
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;

import java.security.AccessController;
import java.security.PrivilegedExceptionAction;
import java.security.PrivilegedActionException;
import java.lang.reflect.Method;

import org.apache.lucene.util.Constants;

/** File-based {@link Directory} implementation that uses
 *  mmap for reading, and {@link
 *  FSDirectory.FSIndexOutput} for writing.
 *
 * <p><b>NOTE</b>: memory mapping uses up a portion of the
 * virtual memory address space in your process equal to the
 * size of the file being mapped.  Before using this class,
 * be sure your have plenty of virtual address space, e.g. by
 * using a 64 bit JRE, or a 32 bit JRE with indexes that are
 * guaranteed to fit within the address space.
 * On 32 bit platforms also consult {@link #setMaxChunkSize}
 * if you have problems with mmap failing because of fragmented
 * address space. If you get an OutOfMemoryException, it is recommended
 * to reduce the chunk size, until it works.
 *
 * <p>Due to <a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4724038">
 * this bug</a> in Sun's JRE, MMapDirectory's {@link IndexInput#close}
 * is unable to close the underlying OS file handle.  Only when GC
 * finally collects the underlying objects, which could be quite
 * some time later, will the file handle be closed.
 *
 * <p>This will consume additional transient disk usage: on Windows,
 * attempts to delete or overwrite the files will result in an
 * exception; on other platforms, which typically have a &quot;delete on
 * last close&quot; semantics, while such operations will succeed, the bytes
 * are still consuming space on disk.  For many applications this
 * limitation is not a problem (e.g. if you have plenty of disk space,
 * and you don't rely on overwriting files on Windows) but it's still
 * an important limitation to be aware of.
 *
 * <p>This class supplies the workaround mentioned in the bug report
 * (see {@link #setUseUnmap}), which may fail on
 * non-Sun JVMs. It forcefully unmaps the buffer on close by using
 * an undocumented internal cleanup functionality.
 * {@link #UNMAP_SUPPORTED} is <code>true</code>, if the workaround
 * can be enabled (with no guarantees).
 * <p>
 * <b>NOTE:</b> Accessing this class either directly or
 * indirectly from a thread while it's interrupted can close the
 * underlying channel immediately if at the same time the thread is
 * blocked on IO. The channel will remain closed and subsequent access
 * to {@link MMapDirectory} will throw a {@link ClosedChannelException}. 
 * </p>
 */
public class MMapDirectory extends FSDirectory {
    private boolean useUnmapHack = UNMAP_SUPPORTED;
    public static final int DEFAULT_MAX_BUFF = Constants.JRE_IS_64BIT ? (1 << 30) : (1 << 28);
    private int chunkSizePower;

    /** Create a new MMapDirectory for the named location.
     *
     * @param path the path of the directory
     * @param lockFactory the lock factory to use, or null for the default
     * ({@link NativeFSLockFactory});
     * @throws IOException
     */
    public MMapDirectory(File path, LockFactory lockFactory) throws IOException {
        super(path, lockFactory);
        setMaxChunkSize(DEFAULT_MAX_BUFF);
    }

    /** Create a new MMapDirectory for the named location and {@link NativeFSLockFactory}.
     *
     * @param path the path of the directory
     * @throws IOException
     */
    public MMapDirectory(File path) throws IOException {
        super(path, null);
        setMaxChunkSize(DEFAULT_MAX_BUFF);
    }

    /**
     * <code>true</code>, if this platform supports unmapping mmapped files.
     */
    public static final boolean UNMAP_SUPPORTED;
    static {
        boolean v;
        try {
            Class.forName("sun.misc.Cleaner");
            Class.forName("java.nio.DirectByteBuffer").getMethod("cleaner");
            v = true;
        } catch (Exception e) {
            v = false;
        }
        UNMAP_SUPPORTED = v;
    }

    /**
     * This method enables the workaround for unmapping the buffers
     * from address space after closing {@link IndexInput}, that is
     * mentioned in the bug report. This hack may fail on non-Sun JVMs.
     * It forcefully unmaps the buffer on close by using
     * an undocumented internal cleanup functionality.
     * <p><b>NOTE:</b> Enabling this is completely unsupported
     * by Java and may lead to JVM crashes if <code>IndexInput</code>
     * is closed while another thread is still accessing it (SIGSEGV).
     * @throws IllegalArgumentException if {@link #UNMAP_SUPPORTED}
     * is <code>false</code> and the workaround cannot be enabled.
     */
    public void setUseUnmap(final boolean useUnmapHack) {
        if (useUnmapHack && !UNMAP_SUPPORTED)
            throw new IllegalArgumentException("Unmap hack not supported on this platform!");
        this.useUnmapHack = useUnmapHack;
    }

    /**
     * Returns <code>true</code>, if the unmap workaround is enabled.
     * @see #setUseUnmap
     */
    public boolean getUseUnmap() {
        return useUnmapHack;
    }

    /**
     * Try to unmap the buffer, this method silently fails if no support
     * for that in the JVM. On Windows, this leads to the fact,
     * that mmapped files cannot be modified or deleted.
     */
    final void cleanMapping(final ByteBuffer buffer) throws IOException {
        if (useUnmapHack) {
            try {
                AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                    public Object run() throws Exception {
                        final Method getCleanerMethod = buffer.getClass().getMethod("cleaner");
                        getCleanerMethod.setAccessible(true);
                        final Object cleaner = getCleanerMethod.invoke(buffer);
                        if (cleaner != null) {
                            cleaner.getClass().getMethod("clean").invoke(cleaner);
                        }
                        return null;
                    }
                });
            } catch (PrivilegedActionException e) {
                final IOException ioe = new IOException("unable to unmap the mapped buffer");
                ioe.initCause(e.getCause());
                throw ioe;
            }
        }
    }

    /**
     * Sets the maximum chunk size (default is {@link Integer#MAX_VALUE} for
     * 64 bit JVMs and 256 MiBytes for 32 bit JVMs) used for memory mapping.
     * Especially on 32 bit platform, the address space can be very fragmented,
     * so large index files cannot be mapped.
     * Using a lower chunk size makes the directory implementation a little
     * bit slower (as the correct chunk may be resolved on lots of seeks)
     * but the chance is higher that mmap does not fail. On 64 bit
     * Java platforms, this parameter should always be {@code 1 << 30},
     * as the address space is big enough.
     * <b>Please note:</b> This method always rounds down the chunk size
     * to a power of 2.
     */
    public final void setMaxChunkSize(final int maxChunkSize) {
        if (maxChunkSize <= 0)
            throw new IllegalArgumentException("Maximum chunk size for mmap must be >0");
        //System.out.println("Requested chunk size: "+maxChunkSize);
        this.chunkSizePower = 31 - Integer.numberOfLeadingZeros(maxChunkSize);
        assert this.chunkSizePower >= 0 && this.chunkSizePower <= 30;
        //System.out.println("Got chunk size: "+getMaxChunkSize());
    }

    /**
     * Returns the current mmap chunk size.
     * @see #setMaxChunkSize
     */
    public final int getMaxChunkSize() {
        return 1 << chunkSizePower;
    }

    /** Creates an IndexInput for the file with the given name. */
    @Override
    public IndexInput openInput(String name, int bufferSize) throws IOException {
        ensureOpen();
        File f = new File(getDirectory(), name);
        RandomAccessFile raf = new RandomAccessFile(f, "r");
        try {
            return new MMapIndexInput("MMapIndexInput(path=\"" + f + "\")", raf, chunkSizePower);
        } finally {
            raf.close();
        }
    }

    // Because Java's ByteBuffer uses an int to address the
    // values, it's necessary to access a file >
    // Integer.MAX_VALUE in size using multiple byte buffers.
    private final class MMapIndexInput extends IndexInput {

        private ByteBuffer[] buffers;

        private final long length, chunkSizeMask, chunkSize;
        private final int chunkSizePower;

        private int curBufIndex;

        private ByteBuffer curBuf; // redundant for speed: buffers[curBufIndex]

        private boolean isClone = false;

        MMapIndexInput(String resourceDescription, RandomAccessFile raf, int chunkSizePower) throws IOException {
            super(resourceDescription);
            this.length = raf.length();
            this.chunkSizePower = chunkSizePower;
            this.chunkSize = 1L << chunkSizePower;
            this.chunkSizeMask = chunkSize - 1L;

            if (chunkSizePower < 0 || chunkSizePower > 30)
                throw new IllegalArgumentException("Invalid chunkSizePower used for ByteBuffer size: " + chunkSizePower);

            if ((length >>> chunkSizePower) >= Integer.MAX_VALUE)
                throw new IllegalArgumentException("RandomAccessFile too big for chunk size: " + raf.toString());

            // we always allocate one more buffer, the last one may be a 0 byte one
            final int nrBuffers = (int) (length >>> chunkSizePower) + 1;

            //System.out.println("length="+length+", chunkSizePower=" + chunkSizePower + ", chunkSizeMask=" + chunkSizeMask + ", nrBuffers=" + nrBuffers);

            this.buffers = new ByteBuffer[nrBuffers];

            long bufferStart = 0L;
            FileChannel rafc = raf.getChannel();
            for (int bufNr = 0; bufNr < nrBuffers; bufNr++) {
                int bufSize = (int) ((length > (bufferStart + chunkSize)) ? chunkSize : (length - bufferStart));
                this.buffers[bufNr] = rafc.map(MapMode.READ_ONLY, bufferStart, bufSize);
                bufferStart += bufSize;
            }
            seek(0L);
        }

        @Override
        public byte readByte() throws IOException {
            try {
                return curBuf.get();
            } catch (BufferUnderflowException e) {
                do {
                    curBufIndex++;
                    if (curBufIndex >= buffers.length) {
                        throw new IOException("read past EOF: " + this);
                    }
                    curBuf = buffers[curBufIndex];
                    curBuf.position(0);
                } while (!curBuf.hasRemaining());
                return curBuf.get();
            }
        }

        @Override
        public void readBytes(byte[] b, int offset, int len) throws IOException {
            try {
                curBuf.get(b, offset, len);
            } catch (BufferUnderflowException e) {
                int curAvail = curBuf.remaining();
                while (len > curAvail) {
                    curBuf.get(b, offset, curAvail);
                    len -= curAvail;
                    offset += curAvail;
                    curBufIndex++;
                    if (curBufIndex >= buffers.length) {
                        throw new IOException("read past EOF: " + this);
                    }
                    curBuf = buffers[curBufIndex];
                    curBuf.position(0);
                    curAvail = curBuf.remaining();
                }
                curBuf.get(b, offset, len);
            }
        }

        @Override
        public int readInt() throws IOException {
            try {
                return curBuf.getInt();
            } catch (BufferUnderflowException e) {
                return super.readInt();
            }
        }

        @Override
        public long readLong() throws IOException {
            try {
                return curBuf.getLong();
            } catch (BufferUnderflowException e) {
                return super.readLong();
            }
        }

        @Override
        public long getFilePointer() {
            return (((long) curBufIndex) << chunkSizePower) + curBuf.position();
        }

        @Override
        public void seek(long pos) throws IOException {
            // we use >> here to preserve negative, so we will catch AIOOBE:
            final int bi = (int) (pos >> chunkSizePower);
            try {
                final ByteBuffer b = buffers[bi];
                b.position((int) (pos & chunkSizeMask));
                // write values, on exception all is unchanged
                this.curBufIndex = bi;
                this.curBuf = b;
            } catch (ArrayIndexOutOfBoundsException aioobe) {
                if (pos < 0L) {
                    throw new IllegalArgumentException("Seeking to negative position: " + this);
                }
                throw new IOException("seek past EOF");
            } catch (IllegalArgumentException iae) {
                if (pos < 0L) {
                    throw new IllegalArgumentException("Seeking to negative position: " + this);
                }
                throw new IOException("seek past EOF: " + this);
            }
        }

        @Override
        public long length() {
            return length;
        }

        @Override
        public Object clone() {
            if (buffers == null) {
                throw new AlreadyClosedException("MMapIndexInput already closed: " + this);
            }
            final MMapIndexInput clone = (MMapIndexInput) super.clone();
            clone.isClone = true;
            clone.buffers = new ByteBuffer[buffers.length];
            // Since most clones will use only one buffer, duplicate() could also be
            // done lazy in clones, e.g. when adapting curBuf.
            for (int bufNr = 0; bufNr < buffers.length; bufNr++) {
                clone.buffers[bufNr] = buffers[bufNr].duplicate();
            }
            try {
                clone.seek(getFilePointer());
            } catch (IOException ioe) {
                throw new RuntimeException("Should never happen: " + this, ioe);
            }
            return clone;
        }

        @Override
        public void close() throws IOException {
            try {
                if (isClone || buffers == null)
                    return;
                for (int bufNr = 0; bufNr < buffers.length; bufNr++) {
                    // unmap the buffer (if enabled) and at least unset it for GC
                    try {
                        cleanMapping(buffers[bufNr]);
                    } finally {
                        buffers[bufNr] = null;
                    }
                }
            } finally {
                buffers = null;
            }
        }
    }
}
